Acetylation of textile articles of cellulose

ABSTRACT

The heterogeneous acetylation of regenerated cellulose textile articles is carried out using acetic anhydride as the acetylating agents and an alkali metal acetate, especially potassium acetate, as catalyst at 100*-135* C., keeping the acetic anhydride content of the acetylation bath above 95 percent by weight, and also keeping the constituent filaments of the articles at constant length. The process is quick and thus suitable for continuous operation, and avoids mutual cohesion of the filaments as a result of softening or partial solution.

United States Patent Rajon [15] 3,655,326 [451 Apr. 11, 1972 [54] ACETYLATION OF TEXTILE ARTICLES OF CELLULOSE [72] Inventor: Andre France [73] Assignee: Societe Rhodiaceta, Paris, France [22] Filed: Nov. 5, 1969 [21] Appl. No.: 874,366

Rajon, Tassin-la-Demi-Lune,

[30] Foreign Application Priority Data Nov. 6, 1968 France ..l72765 [52] US. Cl ..8/121, 260/227 [51] Int. Cl. ..D06m 13/20, C08b 3/06 [58] Field of Search ..8/121;260/227 Primary ExaminerGeorge F. Lesmes Assistant ExaminerHarold Wolman Attomey-Stevens, Davis, Miller & Mosher [5 7] ABSTRACT The heterogeneous acetylation of regenerated cellulose textile articles is carried out using acetic anhydride as the acetylating agents and an alkali metal acetate, especially potassium acetate, as catalyst at l00135 C., keeping the acetic anhydride content of the acetylation bath above 95 percent by weight, and also keeping the constituent filaments of the articles at constant length. The process is quick and thus suitable for continuous operation, and avoids mutual cohesion of the filaments as a result of softening or partial solution.

6 Claims, No Drawings ACETYLATION OF TEXTILE ARTICLES OF CELLULOSE The invention relates to the production of textile articles of cellulose acetate by acetylation of textile articles of regenerated cellulose, without going through the stage of dissolving the cellulose. This method of acetylation, in which the structures are preserved, is generally called heterogeneous acetylation.

It is known to acetylate cellulose fibers heterogeneously by treating them with liquid acetic anhydride by itself or mixed with acetic acid at a temperature which is generally between 100 and 135 C., in the presence of potassium acetate as an acetylation catalyst. If, using this process, cellulose fibers are acetylated up to a combined acetic acid content above 45 percent, considerable partial dissolution or softening of the acetylated fibers in the acetylation bath occurs, causing the fibers to stick together. This partial dissolution is generally the greater, the higher the content of combined acetic acid in the acetylated fibers and the higher the temperature of the acetylation bath.

In order to avoid this partial dissolution of the acetylated fibers it has been proposed to add to the acetic anhydride used for the acetylation considerable amounts of a diluent which is a non-solvent for the cellulose acetate formed and is miscible with acetic anhydride, for example benzene, xylene, toluene, decahydronaphthalene or white spirit. However this addition of a diluent to the acetylation bath makes the separation and recovery, from this bath, of the acetic acid produced by the reaction and the unreacted acetic anhydride much more complex and consequently more expensive.

It has furthermore been proposed to avoid the partial dissolution of the filaments, without using a diluent, by carrying out the acetylation in the presence of an only moderately active acetylation catalyst, such as phosphoric acid, employing an acetylation bath containing considerable amounts of acetic acid and more than three times as much acetic anhydride as is theoretically required. However, this process requires a long duration, of the order of 3 hours, for the acetylation, which makes it practically impossible to use it continuously.

The present invention provides a new process of heterogeneous acetylation which makes it possible, without using a diluent, to acetylate textile articles of regenerated cellulose up to a combined acetic acid content between 50 percent and 62.5 percent without partial dissolution of the acetylated articles, and in less than 10 minutes.

The process of the invention comprises treating textile articles of regenerated cellulose, at a temperature between 100 C. and 135 C., and in the presence of an alkali metal acetate, with a bath containing more than 95 percent by weight of acetic anhydride, keeping the acetic anhydride content constantly above 95 percent by weight by removing impurities formed and introducing fresh acetic anhydride, and maintaining the constituent filaments of the articles at a substantially constant length throughout the treatment.

The acetylation can be carried out on various cellulose textile articles, for example yarns, tows, woven fabrics or knitted fabrics of regenerated cellulose which does not possess a fibrillar structure, or of Polynosic regenerated cellulose having a fibrillar and oriented micro-structure. It can be carried out discontinuously but because the time required for the acetylation is short it is particularly advantageous to carry out the process continuously.

Since the constituent filaments of the cellulose textile articles tend to shrink once they are brought into contact with the hot acetic anhydride, it is necessary to apply a certain tension to them in order to maintain their length substantially constant. When yarns or tows are acetylated continuously, it is easy to keep the length of the constituent filaments substantially constant throughout the acetylation by causing the articles to leave the acetylation bath at essentially the same speed as that at which they enter the bath. When woven or knitted fabrics are continuously acetylated it is additionally necessary to keep their width constant throughout the acetylation by means of some appropriate device. Such devices are well known.

Potassium acetate is preferably employed as the alkali metal acetate catalyst and is used in aknown manner; preferably, it is incorporated in the textile articles before the acetylation by passing them continuously through an aqueous solution, preferably saturated, of the potassium acetate, and then drying them with hot air, for example at a temperature of 150 to 180 C. for 1 to 2 minutes. The impregnated articles preferably contain to 180 g. of potassium acetate per 100 g. of cellulose.

The bath used for the acetylation must contain more than percent by weight of acetic anhydride, and preferably contains 99 percent of acetic anhydride and 1 percent of acetic acid. In the acetylation acetic anhydride is consumed and acetic acid formed; part of this acetic acid combines with potassium acetate in the bath to yield a complex compound of potassium acetate and acetic acid.

The acetic anhydride content of the acetylation bath can be maintained above 95 percent by any continuously operating system which allows acetic anhydride to be replaced at the rate at which it is consumed, and the acetic acid produced by the acetylation to be removed, either in the form of free acid or in the form of a complex compound of potassium acetate and acetic acid.

In one advantageous procedure free acetic anhydride is introduced into the acetylation bath, and an equivalent amount of the bath is continuously withdrawn throughout the duration of the treatment.

After leaving the acetylation bath, the acetylated articles are treated according to known processes to free them from unreacted acetic anhydride, free acetic acid and the complex compound of potassium acetate and acetic acid with which they may still be contaminated. This can be done, for example, by treating them first with benzene to remove the acetic anhydride and then with water to remove any acetic acid and its complex compound with potassium acetate, and finally drying them in an oven at a temperature of about 100 C. The acetylated articles can alternatively be treated, as they leave the acetylation bath, with a stream of hot air at a temperature between and 150 C. for a period which can be between 2 and 7 minutes so as to evaporate the acetic anhydride, then washed with water to remove any acetic acid and its complex compound with potassium acetate, and finally dried in an oven at a temperature of about 1 10 C.

The acetylated articles so obtained have suffered no partial dissolution while passing through the acetylation bath, andsubstantially retain the mechanical properties of the initial cellulose articles.

Woven fabrics treated according to the invention or prepared from yarns obtained according to the invention have a good rub resistance, especially if their combined acetic acid content is above 55 percent. They can be washed very easily and their dyeing affinity for plastosoluble dyestuffs is excellent.

The Examples which follow illustrate the invention.

EXAMPLE 1 A continuous treatment is carried out on a tow of continuous Polynosic cellulose filaments having the following characteristics: gauge per strand: 1.06 dtex (0.96 denier); total gauge: 6,700 dtex (6,000 den); tenacity per strand; 5.4 g.; elongation at break 15 percent.

This tow initially passes into a saturated aqueous solution of potassium acetate at 25 C. After drying at 150 C. in air for 2 minutes, it contains g. of potassium acetate per 100 g. of dry cellulose.

The tow impregnated with potassium acetate thereafter passes for 3 minutes through an acetic anhydride bath maintained at 130 C. The devices for driving the tow on entering and leaving the acetylation bath are adjusted to the same speed so that the tow retains a constant length in the acetylation bath. The bath used for the acetylation initially contains 99 percent by weight of acetic anhydride and 1 percent by weight of acetic acid. Its acetic anhydride content is kept at 96 percent throughout the operation by continuously adding acetic anhydride and withdrawing an equivalent amount of acetylation bath.

After issuing from the acetylation bath, the tow is first washed with benzene and then with water to remove completely the uncombined acetic anhydride and the catalyst present in the tow, and is finally dried by means of a stream of hot air at 1 C. for about 4 minutes.

The tow treated in this way has suffered no partial dissolution and individual filaments do not stick; it has a combined acetic acid content of 55.8 percent, a gauge per strand of 1.64 dtex 1.48 denier), a tenacity per strand of 4.6 g. and an elongation at break of 16.8 percent; thus its mechanical characteristics are close to those of the initial tow.

EXAMPLES 2 TO 7 A continuous treatment is carried out on a tow of Polynosic cellulose filaments, having the following characteristics: gauge per strand: 1.40 dtex (1.26 denier); total gauge: 17,000 dtex (15,000 denier); tenacity per strand: 6.4 g; elongation at break: 12 percent.

The tow is initially impregnated with potassium acetate, then dried and thereafter acetylated at constant length according to the process described in Example 1, varying the amount of potassium acetate taken up by the tow as well as the duration and temperature of the acetylation.

On leaving the acetylation bath the tow, which has suffered no partial dissolution and whose fibers do not stick, is dried by means of a stream of hot air at 130 C. for about 3 minutes, washed with water and finally dried at 110 C. for about 4 minutes.

The Table below indicates, for each of these Examples, the amount of potassium acetate with which the tow is impregnated before acetylation, the temperature and duration of the acetylation, and the combined acetic acid content and mechanical characteristics of the tow after acctylation.

Example No.

Potassium acetate taken up (per. 185 150 175 185 150 150 100 g. of cellulose) weight in g. Temperature of the acetic 211111)" 110 115 125 120 114 117 dride, C. Duration of travel in acetic anhy- 5 5 3 3 5 5 dride, in minutes. Properties of product Combined acetic acid content (in 51.5 52.7 56.9 57.1 57.2 59

percentage by weight). Guage per strand:

In dtex 2.14 2.21 2.11 2.30 2. 46 2.46 In denier 1. 93 1. 99 1.90 2.07 2.22 2.22 Tenacity per strand in g 6. 3 6. 7 6. 4 7. 4 5. 9 Elongation at break, percent 13 1 12. 2 14. 1 13 10. 9 12. 3

EXAMPLES 8 TO 12 A continuous treatment is carried out by the same process as in Examples 2 to 7, on a tow of Polynosic cellulose filaments having the following characteristics: gauge per strand: 1.56 dtex, (1.40 denier); total gauge: 20,000 dtex (18,000 denier); tenacity per strand: 7.7 g; elongation at break: 16.8 percent.

On leaving the acetylation bath the tow, which has suffered no partial dissolution and whose fibers do not stick, is dried by a stream of air at! 30 C. for about 7 minutes.

The Table below shows, for each of these Examples, the amount of potassium acetate with which the tow is impregnated before acetylation, the temperature and duration of the acetylation, and the combined acetic acid content and mechanical characteristics of the tow after acetylation.

Example N o.

Potassium acetate taken up (per g. of 87 155 155 150 172 cellulose) weight in g. Temperature of the acetic anhydrlde, C. 115 112 115 117 Duration of the acetylation, in minutes... 6 6 5 6 5 Properties 01 product Combined acetic acid content (in per- 53. 8 55. 4 56.8 58. 3 59. 9

centage by weight). Guage per strand:

In (ltex 2. 30 2. 05 2. l2 2. 71 2. 61 In denicr t 2.15 1.84 1.90 2.44 2.35 Tenacity per strand in g 7. 5 7. 9 6. 2 7. 8 7. 7 Elongation at break, percent.-. 16. 6 15 13. 3 12.5 12. 7

1 claim:

1. A process for the production of cellulose acetate textile articles having a combined acetic acid content of 50-625 percent by the heterogeneous acetylation of regenerated cellulose textile articles, which comprises treating the said regenerated cellulose textilc articles at a temperature of 100-l35 C. and in the presence of at least 80 percent of an alkali metal acetate, based on the weight of cellulose, with a bath which initially and at all times contains more than 95 percent by weight of acetic anhydride, the balance consisting essentially of acetic acid, as such or in the form of a complex with an alkali metal acetate with or without other by-products of the heterogeneous acetylation, maintaining the acetic anhydride content of the bath at all times above 95 percent by weight by removing acetic acid and other by-products and introducing fresh acetic anhydride in the course of the process, and keeping the constituent filaments of the textile articles at a substantially constant length throughout the process by holding them under a tension sufficient to prevent shrinkage, said bath treatment taking less than 10 minutes to obtain the aforesaid combined acetic acid content.

2. Process according to claim 1, in which the textile articles comprise Polynosic regenerated cellulose fibers.

3. Process according to claim 1, in which potassium acetate is used as the alkali metal acetate.

4. Process according to claim 3 in which the textile article is impregnated with 80-180 percent of potassium acetate, based on the weight of the cellulose.

5. Process according to claim 1 in which the process is carried out continuously be passing the regenerated cellulose textile articles through a bath of an aqueous solution of the alkali metal acetate, drying them, passing them into the acetic anhydride bath while keeping their dimensions substantially constant, removing them from the bath, and freeing them substantially from unreacted acetic anhydride and from alkali metal acetate and acetic acid.

6. Process according to claim 4 in which the process is carried out continuously be passing the regenerated cellulose textile articles through a bath of an aqueous solution of the alkali metal acetate, drying them, passing them into the acetic anhydride bath while keeping their dimensions substantially constant, removing them from the bath, and freeing them substantially from unreacted acetic anhydride, and from the complex salt of acetic acid and potassium acetate which is formed in the process. 

2. Process according to claim 1, in which the textile articles comprise Polynosic regenerated cellulose fibers.
 3. Process according to claim 1, in which potassium acetate is used as the alkali metal acetate.
 4. Process according to claim 3 in which the textile article is impregnated with 80-180 percent of potassium acetate, based on the weight of the cellulose.
 5. Process according to claim 1 in which the process is carried out continuously be passing the regenerated cellulose textile articles through a bath of an aqueous solution of the alkali metal acetate, drying them, passing them into the acetic anhydride bath while keeping their dimensions substantially constant, removing them from the bath, and freeing them substantially from unreacted acetic anhydride and from alkali metal acetate and acetic acid.
 6. Process according to claim 4 in which the process is carried out continuously be passing the regenerated cellulose textile articles through a bath of an aqueous solution of the alkali metal acetate, drying them, passing them into the acetic anhydride bath while keeping their dimensions substantially constant, removing them from the bath, and freeing them substantially from unreacted acetic anhydride, and from the complex salt of acetic acid and potassium acetate which is formed in the process. 